How to Add to a Selection in Paint.NET

In Paint.NET, building complex selections often requires combining multiple shapes rather than drawing them all at once. The specific feature that enables you to expand an existing active selection is the Add (Union) selection mode. By activating this mode, any new selection you make merges seamlessly into your current selection boundaries, allowing you to highlight non-contiguous areas or build intricate shapes without starting over.

The Add (Union) Selection Mode

When you activate any selection tool in Paint.NET—such as the Rectangle Select, Lasso Select, Ellipse Select, or Magic Wand—the Tool Bar at the top of the window displays selection options.

Among these options is the Selection Mode dropdown, which defaults to "Replace." To add to your current selection, change this setting to Add (Union). In this mode, any subsequent selection you draw will combine with whatever is already selected on the canvas.

How to Use Add Mode via the Toolbar

  1. Choose your preferred selection tool from the Tools palette (e.g., Lasso or Magic Wand).
  2. Look at the Tool Bar at the top of the screen to find the Selection Mode icon (represented by two overlapping blue squares merged together).
  3. Click the dropdown menu and select Add (Union).
  4. Click or drag over the canvas. The newly outlined region will be added to your existing selection outline.

Keyboard Shortcut for Quick Adding

You do not need to manually change the toolbar setting every time you want to add to a selection. Paint.NET includes a built-in shortcut:

  • Hold down the Ctrl key while making a selection using any selection tool.
  • While the Ctrl key is held, the tool temporarily functions in Add (Union) mode, regardless of which mode is active in the toolbar.
  • Release the mouse button before releasing the Ctrl key to lock in the merged selection.

This shortcut works with all selection tools, including the Magic Wand, making it easy to click multiple separate color regions across an image and combine them into a single active selection.